Release of angiotensin in the paraventricular nucleus in response to hyperosmotic stimulation in conscious rats: a microdialysis study

Brain ACE2 activation following brain aminopeptidase A blockade by firibastat in salt-dependent hypertension

In the brain, aminopeptidase A (APA), a membrane-bound zinc metalloprotease, generates angiotensin III from angiotensin II. Brain angiotensin III exerts a tonic stimulatory effect on the control of blood pressure (BP) in hypertensive rats and increases vasopressin release. Blocking brain angiotensin III formation by the APA inhibitor prodrug RB150/firibastat normalizes arterial BP in hypertensive deoxycorticosterone acetate (DOCA)-salt rats without inducing angiotensin II accumulation. We therefore hypothesized that another metabolic pathway of brain angiotensin II, such as the conversion of angiotensin II into angiotensin 1-7 (Ang 1-7) by angiotensin-converting enzyme 2 (ACE2) might be activated following brain APA inhibition. We found that the intracerebroventricular (icv) administration of RB150/firibastat in conscious DOCA-salt rats both inhibited brain APA activity and induced an increase in brain ACE2 activity. Then, we showed that the decreases in BP and vasopressin release resulting from brain APA inhibition with RB150/firibastat were reduced if ACE2 was concomitantly inhibited by MLN4760, a potent ACE2 inhibitor, or if the Mas receptor (MasR) was blocked by A779, a MasR antagonist. Our findings suggest that in the brain, the increase in ACE2 activity resulting from APA inhibition by RB150/firibastat treatment, subsequently increasing Ang 1-7 and activating the MasR while blocking angiotensin III formation, contributes to the antihypertensive effect and the decrease in vasopressin release induced by RB150/firibastat. RB150/firibastat treatment constitutes an interesting therapeutic approach to improve BP control in hypertensive patients by inducing in the brain renin-angiotensin system, hyperactivity of the beneficial ACE2/Ang 1-7/MasR axis while decreasing that of the deleterious APA/Ang II/Ang III/ATI receptor axis.

Dysregulation of the Renin-Angiotensin System and the Vasopressinergic System Interactions in Cardiovascular Disorders

Purpose of Review

In many instances, the renin-angiotensin system (RAS) and the vasopressinergic system (VPS) are jointly activated by the same stimuli and engaged in the regulation of the same processes.

Recent Findings

Angiotensin II (Ang II) and arginine vasopressin (AVP), which are the main active compounds of the RAS and the VPS, interact at several levels. Firstly, Ang II, acting on AT1 receptors (AT1R), plays a significant role in the release of AVP from vasopressinergic neurons and AVP, stimulating V1a receptors (V1aR), regulates the release of renin in the kidney. Secondly, Ang II and AVP, acting on AT1R and V1aR, respectively, exert vasoconstriction, increase cardiac contractility, stimulate the sympathoadrenal system, and elevate blood pressure. At the same time, they act antagonistically in the regulation of blood pressure by baroreflex. Thirdly, the cooperative action of Ang II acting on AT1R and AVP stimulating both V1aR and V2 receptors in the kidney is necessary for the appropriate regulation of renal blood flow and the efficient resorption of sodium and water. Furthermore, both peptides enhance the release of aldosterone and potentiate its action in the renal tubules.

Summary

In this review, we (1) point attention to the role of the cooperative action of Ang II and AVP for the regulation of blood pressure and the water-electrolyte balance under physiological conditions, (2) present the subcellular mechanisms underlying interactions of these two peptides, and (3) provide evidence that dysregulation of the cooperative action of Ang II and AVP significantly contributes to the development of disturbances in the regulation of blood pressure and the water-electrolyte balance in cardiovascular diseases.

Angiotensin III: a physiological relevant peptide of the renin angiotensin system

The renin angiotensin system (RAS) is a peptide hormone system that plays an important role in the pathophysiology of various diseases, including congestive heart failure, hypertension, myocardial infarction, and diabetic nephropathy. This has led researchers to focus extensively on this system, leading to the discovery of various peptides, peptidases, receptors and signal transduction mechanisms intrinsic to the RAS. Angiotensinogen (AGT), angiotensin (Ang) II, Ang III, Ang IV, and Ang-(1-7) are the main biologically active peptides of RAS. However, most of the available studies have focused on Ang II as the likely key peptide from the RAS that directly and indirectly regulates physiological functions leading to pathological conditions. However, data from recent studies suggest that Ang III may produce physiologically relevant effects that are similar to those produced by Ang II. Hence, this review focuses on Ang III and the myriad of physiological effects that it produces in the body.

Role of angiotensin II type 1 receptors in the subfornical organ in the pressor responses to central sodium in rats

Central infusion of Na(+)-rich artificial cerebro-spinal fluid (aCSF) activates the brain renin-angiotensin system and causes sympatho-excitatory and pressor responses. We evaluated the role of the subfornical organ (SFO) and angiotensin II type 1 (AT1) receptors in the SFO in mediating the central Na(+)-induced pressor response. In conscious Wistar rats, intra SFO infusions of Na(+)-rich aCSF containing 0.45 and 0.6M Na(+) at 10 nl/min or injection of angiotensin II (Ang II) at 80 ng increased blood pressure (BP) by 15-22 mmHg, whereas mannitol with the same osmolarity as the Na(+)-rich aCSF had no effects. Intra SFO infusion of the AT1 receptor blocker candesartan abolished the pressor response induced by intra SFO administration of Na(+)-rich aCSF or Ang II. Intra cerebro-ventricular (icv) infusion of Na(+)-rich aCSF (0.3M Na(+)) at 3.8 μl/min for 10 min increased BP by 15-20 mmHg. Electrolytic lesion of the SFO attenuated these BP increases by 50-70%. Intra SFO infusion of candesartan also prevented 50% of these pressor responses. These data suggest that SFO neurons are indeed sensitive to Na(+), the SFO is a major - but not only - site in the brain to sense an increase in CSF [Na(+)], and activation of AT1 receptors in the SFO mediates the SFO component of the Na(+)-induced pressor response.

The central mechanism underlying hypertension: a review of the roles of sodium ions, epithelial sodium channels, the renin-angiotensin-aldosterone system, oxidative stress and endogenous digitalis in the brain

The central nervous system has a key role in regulating the circulatory system by modulating the sympathetic and parasympathetic nervous systems, pituitary hormone release, and the baroreceptor reflex. Digoxin- and ouabain-like immunoreactive materials were found >20 years ago in the hypothalamic nuclei. These factors appeared to localize to the paraventricular and supraoptic nuclei and the nerve fibers at the circumventricular organs and supposed to affect electrolyte balance and blood pressure. The turnover rate of these materials increases with increasing sodium intake. As intracerebroventricular injection of ouabain increases blood pressure via sympathetic activation, an endogenous digitalis-like factor (EDLF) was thought to regulate cardiovascular system-related functions in the brain, particularly after sodium loading. Experiments conducted mainly in rats revealed that the mechanism of action of ouabain in the brain involves sodium ions, epithelial sodium channels (ENaCs) and the renin-angiotensin-aldosterone system (RAAS), all of which are affected by sodium loading. Rats fed a high-sodium diet develop elevated sodium levels in their cerebrospinal fluid, which activates ENaCs. Activated ENaCs and/or increased intracellular sodium in neurons activate the RAAS; this releases EDLF in the brain, activating the sympathetic nervous system. The RAAS promotes oxidative stress in the brain, further activating the RAAS and augmenting sympathetic outflow. Angiotensin II and aldosterone of peripheral origin act in the brain to activate this cascade, increasing sympathetic outflow and leading to hypertension. Thus, the brain Na(+)-ENaC-RAAS-EDLF axis activates sympathetic outflow and has a crucial role in essential and secondary hypertension. This report provides an overview of the central mechanism underlying hypertension and discusses the use of antihypertensive agents.

Macrophage migration inhibitory factor in the paraventricular nucleus plays a major role in the sympathoexcitatory response to salt

Central hyperosmotic stimulation (HS) evokes increases in sympathetic nerve activity mediated by activation of angiotensin type 1 receptors in the hypothalamic paraventricular nucleus (PVN). Macrophage inhibitory migration factor (MIF) is an intracellular inhibitory regulator of angiotensin type 1 receptor-mediated actions of angiotensin II within neurons of the PVN. MIF mediates its actions via its intrinsic thiol-protein oxidoreductase activity. We demonstrate that intracerebroventricular injection of hypertonic saline into Sprague-Dawley rats elicits a significant (≈112%) increase in MIF mRNA expression in the PVN. Next, we evaluated the effect of viral-mediated expression of either MIF or [C60S]-MIF (which lacks thiol-protein oxidoreductase activity) in the PVN on the sympathoexcitation evoked by HS. We used a decorticate, arterially perfused in situ preparation of male Wistar rats (60 to 80 g). HS was induced by raising perfusate osmolality from 290 to 380 milliosmoles for 40 seconds. Seven to 10 days before experiments, rats were injected bilaterally (500 nL per side) with 0.9% saline (control) or with adenoassociated virus to express MIF, [C60S]-MIF, or enhanced green fluorescent protein in the PVN. HS produced sympathoexcitation in both the 0.9% saline and enhanced green fluorescent protein groups (sympathetic nerve activity increase of +27±4% and +25±4%, respectively; P<0.05), an effect that was not observed in the MIF group (+4±5%). Conversely, the HS-induced increase in sympathetic nerve activity was potentiated in the [C60S]-MIF group (+45±6%; P<0.05). We propose that MIF acting within the PVN is a major counterregulator of HS-induced sympathoexcitation, an effect that depends on thiol-protein oxidoreductase activity.

Nitric oxide mediates feedback inhibition in angiotensin II-induced upregulation of vasopressin mRNA

Angiotensin II (Ang II) stimulates hypothalamic magnocellular neurons to release arginine vasopressin (AVP) via Ang II type 1 (AT1) receptors during chronic hyperosmotic condition. On the other hand, endogenous nitric oxide (NO) tonically inhibits the activity of AVP producing neurons; and system infusion of Ang II elicits the activity of NO producing neurons in the hypothalamus. These studies suggest that NO may mediate feedback inhibition in Ang II modulation of AVP neuronal excitability. To confirm this hypothesis, we first investigated colocalization of neuronal NO synthase (nNOS) and AT1 receptors in the hypothalamic magnocellular nuclei of adult male rats by using double immunofluorescence. We found that 60% and 65% of AT1 receptors immunoreactive neurons coexpressed nNOS in the hypothalamic paraventricular nucleus and supraoptic nucleus, respectively. We then demonstrated that intracerebroventricular administration of nNOS inhibitor N-omega-nitro-l-arginine methyl ester further enhanced upregulation of AVP mRNA level but totally abolished upregulation of nNOS mRNA level in the paraventricular and supraoptic nuclei of anesthetized rats induced by a prior administration of Ang II. Theses morphological and pharmacological data demonstrate that NO mediates negative feedback regulation of Ang II-induced upregulation of AVP mRNA.

Mechanisms in the PVN mediating local and central sodium-induced hypertension in Wistar rats

Sympathoexcitatory and hypertensive responses to central infusion of Na(+)-rich artificial cerebrospinal fluid (aCSF) are enhanced by aldosterone and mediated by mineralocorticoid receptors (MRs) and benzamil-blockable Na(+) influx, leading to "ouabain" release and ANG II type 1 (AT(1)) receptor stimulation. The present study evaluated the functional role of these mechanisms in the paraventricular nucleus (PVN). In conscious Wistar rats, Na(+)-rich aCSF was infused either directly into the PVN or intracerebroventricularly preceded by aldosterone and blockers. Infusion of Na(+)-rich aCSF in the PVN caused gradual increases in blood pressure (BP) and heart rate (HR). Aldosterone and a subpressor dose of ouabain in the PVN alone did not affect BP and HR but enhanced responses to Na(+). Eplerenone, benzamil, and "ouabain"-binding Fab fragments only blocked the enhancement by aldosterone, whereas losartan blocked all responses to Na(+)-rich aCSF in the PVN. Increases in BP and HR by intracerebroventricular infusion of Na(+)-rich aCSF were enhanced by aldosterone infused intracerebroventricularly, but not in the PVN. Telmisartan in the PVN again blocked all responses. In contrast, both eplerenone and benzamil in the PVN did not change the pressor responses to intracerebroventricular infusion of aldosterone and Na(+)-rich aCSF. These findings indicate that AT(1) receptors in the PVN mediate the responses to Na(+)-rich aCSF and their enhancement by aldosterone, both locally in the PVN or in the general CSF. MRs, benzamil-blockable Na(+) channels or transporters, and "ouabain" can be functionally active in the PVN, but in Wistar rats appear not to contribute to the pressor responses to short-term increases in CSF [Na(+)].

AT(1) and glutamatergic receptors in paraventricular nucleus support blood pressure during water deprivation

Water deprivation activates sympathoexcitatory neurons in the paraventricular nucleus (PVN); however, the neurotransmitters that mediate this activation are unknown. To test the hypothesis that ANG II and glutamate are involved, effects on blood pressure (BP) of bilateral PVN microinjections of ANG II type 1 receptor (AT1R) antagonists, candesartan and valsartan, or the ionotropic glutamate receptor antagonist, kynurenate, were determined in urethane-anesthetized water-deprived and water-replete male rats. Because PVN may activate sympathetic neurons via the rostral ventrolateral medulla (RVLM) and because PVN disinhibition increases sympathetic activity in part via increased drive of AT1R in the RVLM, candesartan was also bilaterally microinjected into the RVLM. Total blockade of the PVN with bilateral microinjections of muscimol, a GABA(A) agonist, decreased BP more (P < 0.05) in water-deprived (-29 +/- 8 mmHg) than in water-replete (-7 +/- 2 mmHg) rats, verifying that the PVN is required for BP maintenance during water deprivation. PVN candesartan slowly lowered BP by 7 +/- 1 mmHg (P < 0.05). In water-replete rats, however, candesartan did not alter BP (1 +/- 1 mmHg). Valsartan also produced a slowly developing decrease in arterial pressure (-6 +/- 1 mmHg; P < 0.05) in water-deprived but not in water-replete (-1 +/- 1 mmHg) rats. In water-deprived rats, PVN kynurenate rapidly decreased BP (-19 +/- 3 mmHg), and the response was greater (P < 0.05) than in water-replete rats (-4 +/- 1 mmHg). Finally, as in PVN, candesartan in RVLM slowly decreased BP in water-deprived (-8 +/- 1 mmHg; P < 0.05) but not in water-replete (-3 +/- 1 mmHg) rats. These data suggest that activation of AT(1) and glutamate receptors in PVN, as well as of AT1R in RVLM, contributes to BP maintenance during water deprivation.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

ANG III induces expression of inducible transcription factors of AP-1 and Krox families in rat brain

In addition to rapid responses comprising increases in blood pressure, drinking, and stimulation of natriuresis, ANG II induces the expression of transcription factors (TF) in the central nervous system. The ANG II metabolite ANG III (ANG 2–8) has been demonstrated to exert physiological effects similar to those of ANG II. We aimed to determine 1) whether ANG III induces TF expression in the brain, 2) which ANG II (AT) receptor subtype is involved, and 3) whether the two peptides, ANG II and ANG III, differ in their efficacy to stimulate TF expression. ANG II (100 pmol), ANG III (100 pmol), or vehicle was injected into the lateral brain ventricle of conscious rats alone or in combination with the AT1 receptor antagonist losartan (10 nmol), the AT2 receptor antagonist PD-123319 (5 nmol), or the aminopeptidase inhibitor amastatin (10 nmol). Similar to ANG II, ANG III induced the expression of c-Fos, c-Jun, and Krox-24 in four brain regions, subfornical organ, median preoptic area, paraventricular nucleus, and supraoptic nucleus of the hypothalamus, with the same efficacy. This effect was AT1 receptor mediated. Pretreatment with amastatin reduced the expression of TF in response to ANG II, indicating that this expression is partly mediated by ANG III. Interestingly, the AT2 receptor antagonist PD-123319 alone slightly enhanced the expression of c-Fos, c-Jun, and Krox-24 in different populations of neurons of the paraventricular nucleus. These data indicate that different populations of neurons in the paraventricular nucleus are tonically inhibited by AT2 receptors under physiological conditions.

Plasma sodium and hypertension

Dietary salt is the major cause of the rise in the blood pressure with age and the development of high blood pressure in populations. However, the mechanisms whereby salt intake raises the blood pressure are not clear. Existing concepts focus on the tendency for an increase in extracellular fluid volume (ECV), but an increased salt intake also induces a small rise in plasma sodium, which increases a transfer of fluid from the intracellular to the extracellular space, and stimulates the thirst center. Accordingly, the rise in plasma sodium is responsible for the tendency for an increase in ECV. Although the change in ECV may have a pressor effect, the associated rise in plasma sodium itself may also cause the blood pressure to rise. There is some evidence in patients with essential hypertension and the spontaneously hypertensive rat (SHR) that plasma sodium may be raised by 1 to 3 mmol/L. An experimental rise in sodium concentration greater than 5 mmol/L induces pressor effects on the brain and on the renin-angiotensin system. Such a rise can also induce changes in cultured vascular tissue similar to those that occur in the vessels of humans and animals on a high sodium diet, independent of the blood pressure. We suggest that a small increase in plasma sodium may be part of the mechanisms whereby dietary salt increases the blood pressure.

Stimulation of cardiac sympathetic nerve activity by central angiotensinergic mechanisms in conscious sheep

Central actions of angiotensin play an important role in cardiovascular control and have been implicated in the pathogenesis of hypertension and heart failure. One feature of centrally or peripherally administered angiotensin is that the bradycardia in response to an acute pressor effect is blunted. It is unknown whether after central angiotensin this is due partly to increased cardiac sympathetic nerve activity (CSNA). We recorded CSNA and arterial pressure in conscious sheep, at least 3 days after electrode implantation. The effects of intracerebroventricular infusions of ANG II (3 nmol/h for 30 min) and artificial cerebrospinal fluid (CSF) (1 ml/h) were determined. The response to intracerebroventricular hypertonic saline (0.6 M NaCl in CSF at 1 ml/h) was examined as there is evidence that hypertonic saline acts via angiotensinergic pathways. Intracerebroventricular angiotensin increased CSNA by 23 +/- 7% (P < 0.001) and mean arterial pressure (MAP) by 7.6 +/- 1.2 mmHg (P < 0.001) but did not significantly change heart rate (n = 5). During intracerebroventricular ANG II the reflex relation between CSNA and diastolic blood pressure was significantly shifted to the right (P < 0.01). Intracerebroventricular hypertonic saline increased CSNA (+9.4 +/- 6.6%, P < 0.05) and MAP but did not alter heart rate. The responses to angiotensin and hypertonic saline were prevented by intracerebroventricular losartan (1 mg/h). In conclusion, in conscious sheep angiotensin acts within the brain to increase CSNA, despite increased MAP. The increase in CSNA may account partly for the lack of bradycardia in response to the increased arterial pressure. The responses to angiotensin and hypertonic saline were losartan sensitive, indicating they were mediated by angiotensin AT-1 receptors.

Angiotensin II stimulates spinally projecting paraventricular neurons through presynaptic disinhibition

Paraventricular nucleus (PVN) neurons that project to the spinal cord are important in the control of sympathetic outflow. Angiotensin II (Ang II) can stimulate PVN neurons, but its cellular mechanisms are not clear. In this study, we determined the effect of Ang II on the excitatory and inhibitory synaptic inputs to spinally projecting PVN neurons. Whole-cell patch-clamp recordings were performed on PVN neurons labeled by a retrograde fluorescence tracer injected into the thoracic spinal cord of rats. Immunocytochemistry labeling revealed that the immunoreactivity of angiotensin type 1 (AT1) receptors was colocalized with a presynaptic marker, synaptophysin, in the PVN. Application of 0.1-5 microm Ang II significantly decreased the amplitude of evoked GABAergic IPSCs in a concentration-dependent manner. Also, Ang II decreased the frequency of miniature IPSCs from 2.56 +/- 0.45 to 1.05 +/- 0.20 Hz (p < 0.05; n = 12), without affecting the amplitude and the decay time constant. The effect of Ang II on miniature IPSCs was blocked by losartan but not PD123319. However, Ang II had no effect on the evoked glutamatergic EPSCs and did not alter the frequency and amplitude of miniature EPSCs at concentrations that attenuated IPSCs. Furthermore, Ang II increased the firing rate of PVN neurons from 3.75 +/- 0.36 to 7.89 +/- 0.85 Hz (p < 0.05; n = 9), and such an effect was abolished by losartan. In addition, Ang II failed to excite PVN neurons in the presence of bicuculline. Thus, this study provides substantial new evidence that Ang II excites spinally projecting PVN neurons by attenuation of GABAergic synaptic inputs through activation of presynaptic AT1 receptors.

Possible involvement of nitric oxide in the central salt-loading-induced cardiovascular responses in conscious rats

The objective of this study was to elucidate the possible involvement of nitric oxide (NO) in the cardiovascular responses induced by central salt loading. Direct perfusion of the hypothalamic paraventricular nucleus (PVN) region with hypertonic saline (0.3 or 0.45 M) was performed in conscious rats by using an in vivo brain microdialysis technique. The extracellular concentration of NO metabolites in the PVN region was measured, as were the blood pressure (BP) and heart rate (HR). Perfusion of 0.45 M saline increased the BP, HR, and NO metabolite levels in the PVN region; however, perfusion of 0.3 M saline enhanced only the level of NO metabolites but did not induce changes in the BP and HR. Next, we determined whether the NO was involved in the cardiovascular responses induced by hypertonic saline. Pretreatment with N(G)-methyl-L-arginine (L-NMMA), an inhibitor of NO synthase, attenuated the increases in the BP and HR induced by direct perfusion of 0.45 M saline, while direct infusion of 3-morpholinosyndnonimine (SIN-1, a NO donor) in the PVN region induced increases in the BP and HR. These results suggest that local perfusion of the PVN region with hypertonic saline elicits a local release of NO, which may be carried out by activating nitric oxide synthase to produce cardiovascular responses.

Cardiovascular changes induced by central hypertonic saline are accompanied by glutamate release in awake rats

To elucidate neurochemical mechanisms responsible for cardiovascular responses induced by central salt loading, we directly perfused the paraventricular nucleus (PVN) of the hypothalamus region with hypertonic saline (0.3 or 0.45 M) by using an in vivo brain microdialysis technique. We then measured the extracellular concentrations of glutamate in the PVN region in conscious rats along with the blood pressure and heart rate. Blood pressure, heart rate, and glutamate levels were increased by perfusion of 0.45 M saline; however, they did not change by perfusion of 0.3 M saline. Next, we examined the possible involvement of glutamate in the cardiovascular responses induced by hypertonic saline. Dizocilpine, a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptor, attenuated the increases of blood pressure and heart rate, although 6-cyano-7-nitroquinoxaline-2,3-dione, an antagonist of the non-NMDA receptor, did not affect the blood pressure and heart rate. Our results show that local perfusion of the hypothalamic PVN region with hypertonic saline elicits a local release of glutamate, which may act via NMDA-type glutamate receptors to produce cardiovascular responses.

Enhanced central response to dehydration in mice lacking angiotensin AT(1a) receptors

The objective was to determine the central nervous system (CNS) responses to dehydration (c-Fos and vasopressin mRNA) in mice lacking the ANG AT(1a) receptor [ANG AT(1a) knockout (KO)]. Control and AT(1a) KO mice were dehydrated for 24 or 48 h. Baseline plasma vasopressin (VP) was not different between the groups; however, the response to dehydration was attenuated in AT(1a) KO (24 +/- 11 vs. 10.6 +/- 2.7 pg/ml). Dehydration produced similar increases in plasma osmolality and depletion of posterior pituitary VP content. Neuronal activation was observed as increases in c-Fos protein and VP mRNA. The supraoptic responses were not different between groups. In the paraventricular nucleus (PVN), c-Fos-positive neurons (57.4 +/- 10.7 vs. 98.4 +/- 7.4 c-Fos cells/PVN, control vs. AT(1a) KO) and VP mRNA levels (1.0 +/- 0.1 vs. 1.4 +/- 0.1 microCi, control vs. AT(1a) KO) were increased with greater responses in AT(1a) KO. A comparison of 1- to 2-day water deprivation showed that plasma VP, brain c-Fos, and VP mRNA returned toward control on day 2, although plasma osmolality remained high. Data demonstrate that AT(1a) KO mice show a dichotomous response to dehydration, reduced for plasma VP and enhanced for PVN c-Fos protein and VP mRNA. The results illustrate the importance of ANG AT(1a) receptors in the regulation of osmotic and endocrine balance.

Hypo-osmolarity stimulates and high sodium concentration inhibits thyrotropin-releasing hormone secretion from rat hypothalamus

The hypothalamic paraventricular nucleus, representing cell bodies in which thyrotropin-releasing hormone is synthesized, and the median eminence, representing nerve terminals, were incubated in vitro. Various hypo- and hyperosmotic solutions were tested to determine osmotic sensitivity of thyrotropin-releasing hormone secretion. High KCl (56 mM) causing membrane depolarization was used as a non-specific control stimulus to induce thyrotropin-releasing hormone secretion. A 30% decrease of medium osmolarity (from 288 to 202 mOsmol/l) increased thyrotropin-releasing hormone secretion from both the paraventricular nucleus and median eminence. A 30% decrease of medium NaCl content by its replacement with choline chloride did not affect basal thyrotropin-releasing hormone secretion. Increasing medium osmolarity with biologically inactive L-glucose did not affect basal or KCl-induced thyrotropin-releasing hormone secretion from either structure. Medium made hyperosmotic (350-450 mOsmol/l) by increasing the NaCl concentration resulted in a dose-dependent decrease of basal thyrotropin-releasing hormone secretion and abolished KCl-induced thyrotropin-releasing hormone secretion. If an osmotically equivalent amount of choline chloride was substituted for NaCl, there was no effect on thyrotropin-releasing hormone secretion, indicating a specific action of Na+. This study indicates a specific sensitivity to high concentrations of Na+ ions of both thyrotropin-releasing hormone-producing parvocellular paraventricular neurons and thyrotropin-releasing hormone-containing nerve terminals in the median eminence.

The renin-angiotensin system and its receptors

The renin-angiotensin system (RAS) plays an important role in blood pressure control and in water and salt homeostasis. It is involved in the pathophysiology of hypertension and structural alterations of the vasculature, kidney, and heart, including neointima formation, nephrosclerosis, postinfarction remodeling, and cardiac left ventricular hypertrophy (LVH). Recently, an increased knowledge of the effector peptides of the RAS, their receptors, and their respective functions has led to a new principle of treatment for hypertension: the inhibition of angiotensin (Ang) II via angiotensin-converting enzyme inhibitors or Ang II-receptor antagonists. In this review, the Ang receptors AT1 and AT2 and the potential roles of shorter angiotensin fragments, including Ang III(2-8), Ang IV(3-8), and Ang(1-7), are discussed.

Dendritic release of vasopressin and oxytocin

In addition to the release of neurotransmitters from their axon terminals, several neuronal populations are able to release their products from their dendrites. The cell bodies and dendrites of vasopressin- and oxytocin-producing neurones are mainly located within the hypothalamic supraoptic and paraventricular nuclei and neuropeptide release within the magnocellular nuclei has been shown in vitro and in vivo. Local release is induced by a range of physiological and pharmacological stimuli, and is regulated by a number of brain areas; locally released peptides are mainly involved in pre- and postsynaptic modulation of the electrical activity of magnocellular neurones. Spatial and temporal differences between peptide release within the nuclei and that from the distant axonal varicosities indicate that the release mechanisms are at least partially independent, supporting the hypothesis of locally regulated dendritic release of vasopressin and oxytocin. In this respect, magnocellular neurones show similarities to other neuronal populations and thus autoregulation of neuronal activity by dendritic neuromodulator release may be a general phenomenon within the brain.

Central losartan blocks natriuretic, vasopressin, and pressor responses to central hypertonic NaCl in sheep

This study investigated the effect of intracerebroventricular administration of the angiotensin AT1 receptor antagonist losartan on the natriuresis, pressor effect, and arginine vasopressin (AVP) secretion caused by intracerebroventricular infusion of either ANG II, hypertonic saline, or carbachol. Losartan (1 mg/h) or artificial cerebrospinal fluid (CSF) was infused into the lateral ventricle before, during, and after infusions of either ANG II at 10 microg/h for 1 h, 0.75 mol/l NaCl at 50 microl/min for 20 min, or carbachol at 1.66 microg/min for 15 min. Intracerebroventricular infusions of ANG II, 0.75 mol/l NaCl, or carbachol caused increases in renal Na+ and K+ excretion, arterial pressure, and plasma AVP levels. Increases in arterial pressure, Na+ excretion, and plasma AVP concentration ([AVP]) in response to intracerebroventricular ANG II or intracerebroventricular 0.75 mol/l NaCl were either abolished or attenuated by intracerebroventricular infusion of losartan but not by intracerebroventricular infusion of artificial CSF or intravenous losartan. Intracerebroventricular losartan did not reduce the increase in plasma [AVP] or arterial pressure in response to intracerebroventricular carbachol, but it did attenuate the natriuretic response to intracerebroventricular carbachol. We conclude that an intracerebroventricular dose of losartan (1 mg/h) that inhibits responses to intracerebroventricular ANG II also inhibits vasopressin secretion, natriuresis, and the pressor response to intracerebroventricular hypertonic saline. These results suggest that common neural pathways are involved in the responses induced by intracerebroventricular administration of ANG II and intracerebroventricular hypertonic NaCl. We propose that intracerebroventricular infusion of hypertonic saline activates angiotensinergic pathways in the central nervous system subserving the regulation of fluid and electrolyte balance and arterial pressure in sheep.

Central angiotensin AT1 and muscarinic receptors in ITF expression on intracerebroventricular NaCl

In the present study, we investigated the expression pattern of the inducible transcription factors (ITF) c-Fos, c-Jun, JunB, JunD, and Krox-24 following intracerebroventricular injections of hyperosmolar saline (0.2, 0.3, and 0.6 M NaCl) and its mediation via angiotensin and/or muscarinic receptors. c-Fos, c-Jun, and Krox-24 were differentially expressed in organum vasculosum laminae terminalis, median preoptic area, subfornical organ (SFO), and paraventricular and supraoptic nuclei. Expression of c-Fos and c-Jun was inhibited by pretreatment with the angiotensin AT1 receptor antagonist losartan (10 and 20 nmol icv) following 0.20 and 0.30 M saline. Pretreatment with atropine (15 nmol icv) inhibited the 0.30 and 0.60 M NaCl-induced expression of c-Fos, c-Jun, and Krox-24 in all areas except the SFO. Coexpression of the ITF with vasopressin and oxytocin, the major effector peptides in osmoregulation, was demonstrated, implying the corresponding genes as putative target genes of the ITF. The results show a highly differentiated ITF expression pattern in the brain mediated by angiotensinergic and muscarinergic pathways, suggesting a finely tuned regulation of target genes.

Identification of metabolic pathways of brain angiotensin II and III using specific aminopeptidase inhibitors: predominant role of angiotensin III in the control of vasopressin release

Angiotensin (Ang) II and Ang III are two peptide effectors of the brain renin-angiotensin system that participate in the control of blood pressure and increase water consumption and vasopressin release. In an attempt to delineate the respective roles of these peptides in the regulation of vasopressin secretion, their metabolic pathways and their effects on vasopressin release were identified in vivo. For this purpose, we used recently developed selective inhibitors of aminopeptidase A (APA) and aminopeptidase N (APN), two enzymes that are believed to be responsible for the N-terminal cleavage of Ang II and Ang III, respectively. Mice received [3H]Ang II intracerebroventricularly (i.c.v.) in the presence or absence of the APN inhibitor, EC33 (3-amino-4-thio-butyl sulfonate) of the APN inhibitor, EC27 (2-amino-pentan-1,5-dithiol). [3H]Ang II and [3H]Ang III levels were evaluated from hypothalamus homogenates by HPLC. EC33 increased the half-life of [3H]Ang II 2.6-fold and completely blocked the formation of [3H]Ang III, whereas EC27 increased the half-life of [3H]Ang III 2.3-fold. In addition, the effects of EC33 and EC27 on Ang-induced vasopressin release were studied in mice. Ang II was injected i.c.v. in the presence or absence of EC33, and plasma vasopressin levels were estimated by RIA. While vasopressin levels were increased 2-fold by Ang II (5 ng), EC33 inhibited Ang II-induced vasopressin release in a dose-dependent manner. In contrast, EC27 injected alone increased in a dose-dependent manner vasopressin levels. The EC27-induced vasopressin release was completely blocked by the coadministration of the Ang receptor antagonist (Sar1-Ala8) Ang II. These results demonstrate for the first time that (i) APA and APN are involved in vivo in the metabolism of brain Ang II and Ang III, respectively, and that (ii) the action of Ang II on vasopressin release depends upon the prior conversion of Ang II to Ang III. This shows that Ang III behaves as one of the main effector peptides of the brain renin-angiotensin system in the control of vasopressin release.

Interaction of vasopressin and angiotensin II in central control of blood pressure and thirst

It is now well recognized that systemically released angiotensin II (Ang II) and arginine vasopressin (AVP) act in concert in regulation of blood pressure and water-electrolyte balance. Numerous studies have also demonstrated that centrally applied Ang II and AVP cause significant alterations of the cardiovascular functions and body fluid balance. Moreover, it has been established that Ang II and AVP are released in the central nervous system during cardiovascular and osmotic disorders and that the cardiovascular regions of the brainstem and the osmoregulatory regions of the forebrain are extensively innervated by the angiotensinergic and vasopressinergic neurons. Some evidence indicates that the angiotensinergic and vasopressinergic system may interact in the central blood pressure control, although the significance of this interaction may differ in various species. Recently, attempts have been made to find out whether centrally released Ang II and AVP may play a role in the regulation of the cardiovascular system under physiological and pathophysiological conditions. With regard to this, the available evidence strongly suggests that the both systems may be involved in regulation of blood pressure under baseline conditions. In addition, the vasopressinergic system appears to be involved in the adjustment of cardiovascular functions to hypovolemia, whereas its role in regulation of blood pressure during the osmotic disorders is less clear. Regulation of blood pressure and heart rate by centrally released AVP under baseline conditions, during hypovolemia and in osmotic disorders is significantly altered in the spontaneously hypertensive rats. It is now well established that centrally applied Ang II and Ang III are potent dipsogenic compounds. There also is evidence that AVP may enhance the osmotic thirst. However, the physiological role of brain-derived AVP and Ang II in the control of water intake awaits further examination. The available evidence from rat studies does not give support to a significant cooperation between central angiotensinergic and vasopressinergic system in regulation of water intake.

Complex activation of inducible transcription factors in the brain of normotensive and spontaneously hypertensive rats following central angiotensin II administration

The effects of intracerebroventricular (i.c.v.) injections of angiotensin II (Ang II) on the expression of inducible transcription factors (ITF) (c-Fos, FosB, c-Jun, JunB, JunD, Krox-20 and Krox-24) in the brain of conscious rats were assessed immunohistochemically using polyclonal antisera. Ang II (1, 10, 100 ng) induced after 90 min a dose-dependent expression of c-Fos, FosB, c-Jun, JunB and Krox-24, which was confined to four specific brain areas, namely the subfornical organ (SFO), median preoptic area (MnPO), paraventricular nucleus (PVN) and supraoptic nucleus (SON). In the above-mentioned regions, JunD exhibited a high basal staining which was not visibly altered by Ang II. Krox 20 was not induced by AnG II. FosB was only induced 4 h after i.c.v. injection of 100 ng Ang II in the MnPO and PVN. The Ang II-AT1 receptor antagonist, losartan, applied i.c.v. 5 min prior to Ang II (100 ng, i.c.v.) prevented the Ang II-induced ITF expression. In spontaneously hypertensive rats (SHR) but not in Wistar rats with nephrogenic hypertension due to aortic banding (WIab), the Ang II-induced expression of c-Fos, and c-Jun was enhanced in all four areas when compared to normotensive Wistar Kyoto (WKY)- and Wistar (WI) rats. The Ang II-induced expression of Krox-24 in the SFO, MnPO and PVN in SHR was also significantly increased when compared to WKY, WI and WIab rats. Our data demonstrate that a stimulation of periventricular Ang II-AT1 receptors induces a temporally and spatially highly differentiated expression pattern of ITFs restricted to four distinct regions of the forebrain involved in blood pressure regulation and body fluid homeostasis. The points to a strictly regulated expression of target genes in the respective regions. The enhanced Ang II-induced expression of ITFs in SHR compared to normotensive controls is not due to elevated blood pressure itself, since it was not observed in secondary hypertensive rats WIab. Thus, the increased sensitivity to Ang II in SHR appears to be genetically determined. The target genes regulated by Ang II-induced ITFs will have to be identified.

Effect of AV3V lesions on Fos expression and cell size increases in magnocellular neurons of the rat hypothalamus during chronic dehydration

The effects of osmotic stimulation on Fos expression and cell size increase in the supraoptic nucleus were evaluated in intact, sham-operated, and AV3V-lesioned rats. Fos-positive neurons were found mainly in the AV3V regions and the hypothalamic magnocellular neurons in the forebrain in dehydrated intact rats. Intraperitoneal injection of hypertonic saline and chronic dehydration induced a significant increase in number of Fos-positive neurons in the supraoptic nucleus of intact and sham-operated rats. AV3V lesions completely abolished the expression of Fos in SON neurons of rats that were intraperitoneally injected with hypertonic saline and were chronically dehydrated. Chronic dehydration increased significantly cell size of the OXT and AVP magnocelluar neurons in intact and sham-operated rats. However, there was no increase in cell size of those in the AV3V-lesioned rats. These results demonstrate that neural input derived from AV3V regions plays a significant role in causing Fos expression and structural changes such as cell size increase in the hypothalamic magnocellular neurons with osmotic stimulation.

Effect of angiotensin AT2 and muscarinic receptor blockade on osmotically induced vasopressin release

Recently, we have shown that angiotensin II-induced AT1 receptor-mediated vasopressin release can be potentiated by blockade of periventricular AT2 receptors. In the present study, we investigated whether the AT2 receptor also exerts an inhibitory effect on osmotically induced vasopressin release. In addition, we tested the effect of the muscarinic receptor antagonist, atropine, on hyperosmolar saline-induced vasopressin release. Plasma vasopressin levels were determined 90 s after intracerebroventricularly applied hyperosmolar saline (0.2, 0.3 and 0.6 M, 5 microliters) with or without intracerebroventricular pretreatment with 1 nmol of the selective AT2 receptor antagonist, PD 123177 (1-(4-amino-3-methylphenyl)methyl-5-diphenylacetyl-4,5,6,7-tetrahy dro- 1H-imidazo[4,5-c]pyridine-6-carboxylic acid-2HCl), or with 15 nmol of the muscarinic receptor antagonist, atropine. PD 123177 potentiated 0.2 M saline-induced vasopressin release (4.7 +/- 0.8 pg/ml vs. 2.2 +/- 0.3 in vehicle-pretreated controls, P < 0.05), did not affect 0.3 M saline-induced vasopressin release (4.3 +/- 0.7 pg/ml vs. 5.4 +/- 0.6 pg/ml in vehicle-pretreated controls) and reduced 0.6 M saline-induced vasopressin release (10.0 +/- 2.3 pg/ml vs. 17.9 +/- 1.8 pg/ml in vehicle-pretreated controls, P < 0.05). Pretreatment with atropine reduced 0.3 M (2.3 +/- 0.6 pg/ml vs. 5.4 +/- 0.9 pg/ml in vehicle-pretreated controls, P < 0.05) and 0.6 M saline-induced AVP release (4.0 +/- 1.5 pg/ml vs. 18.4 +/- 2.4 pg/ml in vehicle-pretreated controls, P < 0.05) but did not affect 0.2 M saline-induced vasopressin release (2.1 +/- 0.4 pg/ml vs. 3.2 +/- 0.8 pg/ml in vehicle-pretreated controls). Our results suggest that the low saline concentration-induced, AT1 receptor-mediated, vasopressin release is under inhibitory control by periventricular AT2 receptors. Following high saline concentrations, a muscarinic mechanism seems to be predominant on which AT2 receptor stimulation acts in a facilitating manner.

Neuroendocrine and cardiovascular effects of serotonin: selective role of brain angiotensin on vasopressin

Central serotonin (5-HT) and angiotensin (ANG II) stimulate arginine vasopressin (AVP), oxytocin (OT), and adrenocorticotropin (ACTH) secretion and increase blood pressure. Studies were conducted in conscious rats to determine whether neuroendocrine activation by 5-HT requires a brain angiotensinergic intermediate pathway. In the first study, ANG II formation was inhibited by the angiotensin-converting enzyme inhibitor enalapril before injection of the 5-HT releaser/uptake inhibitor d-fenfluramine. Fenfluramine (2 mg/kg ip) stimulated AVP, OT, corticosterone, and prolactin (PRL) secretion (P<0.01). Enalapril (60 mg/l in drinking water for 4 days and 10 mg/kg ip 2 h before the rats were killed) inhibited only the AVP response (P<0.01) to d-fenfluramine. In the second study, the effect of intracerebroventricular injection of the 5-HT2A/2C antagonist LY-53857 (10 microgram), or the ANG II AT1 antagonist DuP-753 (10 microgram), on intracerebroventricular 5-HT (10 microgram)-stimulated AVP, OT, ACTH, PRL, renin secretion, mean arterial pressure (MAP) and heart rate (HR) was tested. LY-53857 inhibited the AVP, OT, and ACTH responses to 5-HT (P<0.01), whereas DuP-753 inhibited only the AVP response (P<0.01). Intraventricular injection of 5-HT increased MAP and decreased HR. The MAP response was not affected by LY-53857 or DuP-753, and at no time did MAP decline below starting levels. The decreased HR was inhibited by LY-53857 but not by DuP-753. These results demonstrate that 5-HT-induced AVP secretion is mediated selectively via brain angiotensinergic mechanisms by way of the AT1 receptor.

Angiotensin receptors in the brain

Angiotensin receptors have recently become a focus of scientific interest due to the recent development of specific receptor ligands which allow to distinguish between various angiotensin II receptor subtypes, notably the angiotensin II type 1 receptor (AT1) and angiotensin II type 2 receptor (AT2). Although both receptors belong to the seven transmembrane domain receptor family they feature less than 35% homology and differ in their signal transduction mechanisms and in the effects mediated. In the brain, both angiotensin receptor types and probably some further subtypes are present and have been localized in distinct regions. In the adult brain, the AT1 receptor dominates by far and is responsible for most of the known central actions of angiotensin peptides, for example blood pressure increase, release of vasopressin from the pituitary gland, natriuresis, drinking and induction of immediate early genes in distinct brain areas. Some of the AT1 receptor-mediated effects have been shown to be enhanced by blockade of AT2 receptors in the brain suggesting that the central AT2 receptor can exert an inhibitory control on AT1 receptor-mediated actions in the brain.

Functional role of intrahypothalamic release of oxytocin and vasopressin: consequences and controversies

This brief review of vasopressin (VP) and oxytocin (OT) release into the extracellular space of the supraoptic (SON) and paraventricular (PVN) nuclei focuses on recent data illustrating the significance of their intranuclear release and the potential functional consequences. With the use of in vitro techniques, it has been demonstrated that administration of exogenous OT causes local peptide release and that, in vivo, this facilitates the milk ejection reflex. These findings lead to the idea that endogenous peptides are released into the hypothalamic nuclei. Microperfusion techniques have been used to monitor the dynamics of intranuclear OT and VP release in response to distinct stimuli. It is clear that intranuclear release of OT plays a role during reproductive states (parturition and lactation) and that intranuclear release of VP and OT is involved in osmoregulation. This review discusses 1) the origin of the intranuclearly released peptides, 2) stimuli which cause release into the hypothalamic nuclei, and 3) the function of intranuclear VP and OT, e.g., regulation of local morphology, feedback mechanisms and synchronization, and the possible role in regulating autonomic function and behavior.

Angiotensin II induces a complex activation of transcription factors in the rat brain: expression of Fos, Jun and Krox proteins

We investigated the effects of intracerebroventricular injection of angiotensin II on neuronal immediate early gene-encoded protein synthesis in the brain of conscious rats. The expression of seven immediate early gene-encoded transcription factors (c-Fos, FosB, c-Jun, JunB, JunD, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif/268) was assessed simultaneously. Angiotensin II (1, 10, 100 ng) induced a dose-dependent expression of c-Fos and Krox-24 in the subfornical organ, the median preoptic area and in the paraventricular nucleus and supraoptic nucleus of the hypothalamus, regions known to be involved in the central osmoregulatory and neuroendocrine actions of angiotensin II. FosB expression was induced four hours after icv injection of the highest dose of angiotensin II in the median preoptic area and paraventricular nucleus, c-Jun expression was restricted to the median preoptic area, subfornical organ and paraventricular nucleus, and JunB was only induced in the median preoptic area and subfornical organ. In these above mentioned regions, JunD exhibited a high basal staining, which was not visibly altered by angiotensin II. Krox-20 was not induced by angiotensin II. Intracerebroventricular injections of isotonic saline did not induce immediate early gene expression in any of the above brain areas. The angiotensin II-AT1 receptor antagonist, losartan, applied intracerebroventricular five minutes prior to angiotensin II, prevented the angiotensin II-induced immediate early gene protein expression. Losartan alone had no effects on immediate early gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin as neuromodulator/neurotransmitter in central control of body fluid and electrolyte homeostasis

Stimulation of central angiotensin receptors promotes, among others, drinking behaviour, stimulation of natriuresis and increased release of vasopressin. Angiotensin (ANG II)-containing pathways in the lamina terminalis and the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei, brain areas involved in the regulation of body fluid homeostasis, have been described. All these areas express predominantly AT1 receptors. The drinking response and the vasopressin release to centrally administered ANG II are mediated by AT1 receptors, while AT2 receptors exert inhibitory effects. Evidence for the involvement of the catecholaminergic and angiotensinergic pathways in the PVN and SON in mediating the ANG II-induced release of vasopressin is presented. ANG II is released in the PVN upon local osmotic stimulation and water deprivation. Finally, we present evidence that activation of central angiotensinergic receptors, water deprivation, or hypertonicity induce transcription of immediate-early genes and expression of the respective proteins in the lamina terminalis and in the PVN and SON. The summarized data implicate ANG II as a neuromodulator/neurotransmitter in central control of body fluid and electrolyte homeostasis.

The role of angiotensin II in the regulation of blood flow to choroid plexuses and cerebrospinal fluid formation in the rat

The effect of peripherally administered angiotensin II (AII) on blood flow to choroid plexuses was examined in pentobarbital-anesthetized rats. The indicator fractionation method with 123I- or 125I-N-isopropyl-p-iodoamphetamine as the marker was employed to measure blood flow. Basal blood flow to choroid plexus of the lateral cerebral ventricle (LVCP) (3.19 +/- 0.23 ml g-1 min-1) was lower than that to choroid plexuses of the third (3VCP) and fourth (4VCP) ventricles (3.90 +/- 0.38 and 3.95 +/- 0.36 ml g-1 min-1, respectively). The effect of AII on choroidal blood flow varied depending on peptide dose and anatomical location of the choroidal tissue. AII infused intravenously at rates of 30 and 50 ng kg-1 min-1 decreased blood flow to both LVCP and 4VCP by 12-20%. Both lower (10 ng kg-1 min-1) and higher (100 and 300 ng kg-1 min-1) AII doses did not alter blood flow to LVCP and 4VCP. Blood flow to the 3VCP was not affected by any dose of the peptide used. In comparison, blood flow to cerebral cortex increased by 33% during intravenous AII infusion at a rate of 300 ng kg-1 min-1. The choroidal blood flow-lowering effect of moderate AII doses was abolished by both AT1 (losartan) and AT2 (PD 123319) receptor subtype antagonists (3 mg kg-1 i.v.). To determine whether the hemodynamic changes observed in choroid plexuses with moderate AII doses influence CSF formation, the ventriculocisternal perfusion was performed in rats (under the experimental conditions described) with Blue Dextran 2000 as the indicator.(ABSTRACT TRUNCATED AT 250 WORDS)